Sustain keyer circuitry with sustain time control circuit in electronic musical instrument

ABSTRACT

A sustain keyer circuitry in electronic musical instrument having two field effect transistors connected in series to each other, the source electrode of the first FET being grounded and the gate electrode thereof being adapted to receive tone signals, the drain electrode thereof being connected to the source electrode of the second FET whose drain electrode is connected to the power source via a load resistor, the gate electrode of said second FET being connected to keying means having a key-operated switch and capable of keying the control voltage to be applied to the gate electrode of said second FET, so that, by the keying operation of said key-operated switch, said tone signal is derived across the load resistor, said circuitry being arranged so that the on-off ratio, i.e., the conducting to nonconducting level ratio of the tone signal, is increased substantially whereas, accordingly, the load in a tone generator is reduced. By incorporating, in said sustain keyer circuitry, a sustain time control circuit, i.e., an envelope-forming circuit, which is formed by the use, in a charging and discharging circuit which is employed as the time constant circuit for determining the sustain time of said electronic musical instrument, of a capacitor of a relatively low capacitance and a third FET having an extremely high inner impedance and being used as a variable resistance element, said circuitry can be easily integrated.

United States Patent Hirano 3,637,915 [451 Jan; 25, 1972 [72] Inventor: Katsuhiko Hirano, Hamakita, Japan Primary Examinfl-Thomas Kolma v Assistant Examiner-Stanley J Witkowski [73] Asstgneez Nippon Gakkl Seizo Kabushikl 1 Keisha, Anomey cushman' Darby & cushman Hamamatsu-shi, Shizuoka-ken, Japan 22 Filed: Apr. 9, 1970 5 ABSTRACT 21 A LN 27 A sustain keyer circuitryin electronic musical instrument 1 pp 0 having twofield effect transistors connected in series to each U other, the source electrode of the first FET being grounded [30] Foreign Application Priority Data and the gate electrode thereof being adapted to receive tone signals, the drain electrode thereof being connected to the 2 1; 5: source electrode of the second FET whose drain electrode is 969 Japan 4/35387 connected to the power source via a load resistor, the gate 1969 Japan electrode of said second FET being connected to keying l3 1969 means having a key-operated switch and capable of keying the 1969 J p 44/43960 control voltage to be applied to the gate electrode of said A y 14 1969 J p 44/28924 second FET, so that, by the keying operation of said keyapan operated switch, said tone signal is derived across the load resistor, said circuitry being arranged so that the on-off ratio, (g1. .,.84/l .l3, Le. the conducting to nonconducting level ratio of the tone 58 d 26 signal, is increased substantially whereas, accordingly, the I 1 le 0 A load in a tone generator is reduced. By incorporating, in said sustain keycr circuitry, a sustain time control circuit, i.e., an envelope-forming circuit, which is formed by the use, in a [561 References Cited charging and discharging circuit which is employed as the time UNITED STATES PATENTS constant circuit for determining the sustain time of said electrontc musical instrument, of a capac1tor of a relatively low 3,555,993 2/ Bunger capacitance and a third FET having an extremely high inner 3, 4/1965 Siiefel-mimpedance and being used as a variable resistance element, 3,333,453 8 harp--- .-'.34/1-2 said circuitry can be easily integrated. 3,407,358 10/1968 on... "307 246 x I V 13 Claims, 15 Drawing Figures L 1 I d g C C0 :lrl Q2 F' l l J Q -11 I gt/ U W I 1 w) m 3,414,735 12/1968 Harris et al. ..307/246 X 3,461,325 8/1969 Barrett; ..307/251X 3,535,972 10/1970 Teranishi ..84/1.26

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INVENTOR Mira/Mm 160mm By Gas/WAX, .oA/wy ATTORNEYS SUSTAIN KEYER CIRCUITRY WITII SUSTAIN TIME CONTROL CIRCUIT IN ELECTRONIC MUSICAL INSTRUMENT This application is related to US. application Ser. No. 27,028 filed on Apr. 9, 1970, which related application represents an improvement over the subject matter of this application.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is concerned with a sustain keyer circuitry for use in an electronic musical instrument, and more particularly, it relates to a sustain keyer circuitry provided with a sustain time control circuit and being capable of integrating the circuitry in the electronic musical instrument.

2. Description of the Prior Art Referring to FIG. 1, there is shown a conventional sustain keyer circuitry for use in an electronic musical instrument, which is arranged in such a way that an input terminal t, to which a tone signal of a low frequency derived from a tone generator (not shown) which is comprised of, for example, a flip-flop circuit is applied is connected, via a resistor R,, to the base electrode of a transistor Q, said base electrode being connected, via biasing resistors R and R,,, respectively, to both the ground and the power source V the collector electrode of said transistor being connected, via a resistor R, and a capacitor C,, respectively, to both the ground and a signal output terminal t,, the emitter electrode of said transistor Q being connected, via a series circuit consisting of a resistor R and a capacitor C to the power source V,., the junction r,, of the resistor R and the capacitor C being connected, via a series circuit consisting of a resistor R and a diode D, to a slidable contact r of a variable resistor (potentiometer) R, which, in turn, is interposed between the power sources V, and -V said juncture 5 being connected, via a series circuit consisting of a resistor R and a key-operated switch S, which is adapted to be keyed in association with the depressing actions applied onto the keys of the keyboard of the electronic musical instrument, to the power source V the juncture r between said diode D and said resistor R beingconnected, via another resistor R to the power source V,.

It is to be noted that the sustain keyer circuit SB which is located within the block defined by a-dot-and-a-dash line in FIG. I and which is comprised of such elements as the transistor 0, a resistor and a capacitor, and said input terminal I, are provided respectively in, for example, a console of an electronic musical instrument in a number corresponding to the number, for example, 90 to 100, of the tone generators installed in accordance with the number of the keys of the keyboard of the electronic musical instrument. Whereas, the variable resistor (potentiometer) R-, is provided only one in number so that its slidable contact r is connected in common to the number of said sustain keyer circuits SB corresponding in number to said keys, via the corresponding number of diodes, respectively.

In the known circuitry having the foregoing construction, the respective resistors R, to R, and the respective power sources V and -V,. are arranged beforehand to have preset values in such a way that the transistor 0 may be rendered to its cutoff" state or to its on state by the keying operation performed by the player or the user of the instrument on the key-operated switch S, which is adapted to be keyed in association with the depression applied onto the selected keys of the keyboard of the electronic musical instrument, and along with this, the arrangement is provided to be operative so that, when this key-operated switch S, is closed, the transient characteristic in the course of the beginning of conduction of said transistor Q is determined by a time constant which, in turn, is determined by the capacitance of the capacitor C connected to the emitter circuit of the transistor 0, the resistances of the resistors R and R and the inner resistance between the collector and the emitter electrodes in the conductive state of said transistor 0, to thereby determine the buildup characteristic of the signal detected at the output terminal t, on the collector side thereof, whereas, when the keyoperated switch S, is opened, the transient characteristic of the transistor 0 in its course of the ending of conduction is determined by the time constant which, in turn, is determined by the capacitor C the resistances of the resistors R, and R,, and the value of resistance between the slidable contact of the variable resistor (potentiometer) R and the power source V (or V,), to thereby obtain the decay characteristic (socalled sustain time) of the output signal derived from said output terminal t, in the form of a desired characteristic. Furthermore, in said known circuitry, arrangements are made to eliminate the possible leakage of a signal due to the reverse directional breakdown voltage between the base and emitter electrodes of the transistor 0, the input signal from the tone generator is divided in its voltage by the resistors R, and R and by the resistor R to drop the input voltage applied to the base electrode of said transistor 0 below the base-emitter breakdown voltage, whereas, the input impedance of the sustain keyer circuit SB is elevated by such an element as the resistor R, up to the order of about kiloohms to thereby reduce the loan on the tone generator.

Accordingly, in the circuitry of the prior art, it should be understood that, even when the key-operated switch S, is opened to cut off the transistor Q for shutting ofi the output signal which is detected at the collector side of the transistor 0, there may leak out, through the base and collector electrodes of the transistor Q, a tone signal of a considerably large am plitude which is always applied to the input terminal I, and such a leakage may be thus detected.

Accordingly, in the circuitry of the prior art, it should be noted that, even when the key-operated switch S, is opened to render the transistor Q to the cutofi state and to, thereby, shut off the output signal which is detected at the collector side of said transistor, the tone signal having a considerably large amplitude which is always applied to the input terminal 1, may leak outowing to the effect caused by such reasons as the static capacity between the base and collector electrodes of the transistor Q and the dark current (leakage current) which flows between the collector and emitter electrodes of the transistor-and may be detected at the output terminal I, side via the base and collector electrodes of the transistor Q. Accordingly, the level ratio of the output signal at the on-off time of the transistor 0 (meaning the conducting to nonconducting level ratio of the output signal) due to the keying operation of the key-operated switch S, is obtained only in as low a level of the order as 50-55 db. as shown by the actually measured values which are indicated by the solid curve b in FIG. 3. Therefore, even when the keys of the keyboard of the electronic musical instrument are not depressed at all, there will come out, through the speaker or the like of the instrument, a noise which is very low in loudness but resembles the sound produced when all of the keys of, for example, an organ are depressed. Thus, this sound or noise will become a nuisance when the electronic musical instrument of this type is played. As described, the circuitry of the prior art not only will not permit one to obtain a conducting to nonconducting level ratio which is sufficient for an electronic musical instrument of a large scale having complicated circuitries, but also will make the integration of the circuitry of this type markedly difficult because of the fact that the sustain keyer circuit SB requires a number of resistors. Furthermore, even when an effort is made to lessen the load to be applied on the tone generator by, for example, connecting the resistor R, in series to the input side of the transistor Q in the manner as described previously, there will be obtained as small an input impedance as the order of only 100-200 K!) at best, with the result that there may arise distorted output waveform depending on the type of the tone generator employed, so that the circuitry of the prior art had the serious drawback that the quality of the tone was poor and that there arose a great deal of loss in the output signal which was not economical.

Furthermore, especially in order to obtain a desired sustain effect in the known circuit arrangement by rendering the transistor to its cutoff state by opening the key-operated switch S after the lapse of a predetermined sustain time, it has been necessary, on the one hand, to set the time constant which is determined by such factors as the capacitance of the capacitor C the resistance values of the resistors R and R and the resistance value between the slidable contact r, of the variable resistor R and the power source V (or V,)--so as to assume a considerably large value. Along with this, it has been necessary also, on the other hand, to use the aforesaid capacitor C having a considerably large capacitance, or in other words, it has been necessary to use an electrolytic capacitor having a capacitance of, for example, the order of I00 microfarads, in view of the fact that there is a limit within a certain range in the selection of the values of the aforesaid respective resistors when the transistor 0 is selected so as to display the optimum action with respect to the fixed power sources V and V,. This not only will lead to an increase in the size of the circuitry and an increase in the cost, but also to the following inconvenience. That is to say, since an electrolytic capacitor of this type having a large capacity presents a variance in the value of its static capacitance which is usually in such a large range as from l0 to +200 percent, this variance will directly result in the variance of the aforesaid time constant value. Accordingly, this variance of the time constant will lead to a variance of a large range of the transient characteristic, at the opening of the key-operated switch 8,, of the cutoff signal, which will constitute a great hindrance at the time the electronic musical instrument of this type is played. Also, in view of the necessity for the use of five resistors R to R which are required for the formation of the circuitry, there has been the serious drawback that the integration of the circuitries of this type becomes markedly difficult.

SUMMARY OF THE INVENTION It is, therefore, an object of the present invention to provide a sustain keyer circuit for use in an electronic musical instrument, which improves the conducting to nonconducting level ratio of the signal, by incorporating, in said circuit, two field effect transistors as the switching elements which are connected in series to each other.

Another object of the present invention is to provide a sustain keyer circuit for use in an electronic musical instrument, which improves the safety as well as the reliability of keying operation, and which is especially safe in case of a failure of the action of the instrument due to a short circuit of said transistors, by incorporating, in said circuit, two or more field effect transistors as the switching elements which are connected in series to each other.

Still another object of the present invention is to provide a sustain keyer circuit for use in an electronic musical instrument, which minimizes a wasteful loss of signal in addition to the aforesaid advantages especially the advantage represented by the safety in case of a failure of the action of the instrument due to a short circuit of said transistors, by incorporating, in said circuit, three or'more serial sets of field effect transistors which, in each set, are connected in parallel to each other, said serial sets serving as the switching elements.

A further object of the present invention is to provide a sustain keyer circuit which is capable of producing a prolonged decay time by the use of a capacitor having a small capacitance.

Yet a further object of the present invention is to provide a sustain time control circuit utilizing a field effect transistor for use in an electronic musical instrument.

Still further object of the present invention is to provide a sustain time control circuit for use in an electronic musical instrument, which is of the arrangement that a serial and/or parallel circuit consisting of three field effect transistors is connected in series to a capacitor toform a charging and discharging circuit for use as the time constant circuit intended for determining the sustain time and which is operative so that a desired sustain time may be obtained by varying the DC gate potential of one of said three field effect transistors.

Another object of the present invention is to provide a sustain time control circuit for use in an electronic musical instrument, which permits one to control the sustain time as desired while keeping the envelope within the decay time of the tone signal, i.e., within the so-called sustain time, to assume an exponential damping curve, and whichsimplifies the circuit arrangement by reducing the number of the biasing power sources intended for the field effect transistors.

Still another object of the present invention is to provide a sustain time control circuit for use in an electronic musical instrument, in which a serial and/or parallel circuit consisting of four field effect transistors and being connected in series to a capacitor to form a charging and discharging circuit for determining the sustain time to be operative so that, by simultaneously altering the DC gate potential of each of said transistors in the same direction, a desired sustain time is obtained, while, on the other hand, reducing the number of biasing power sources.

Yet another object of the present invention is to provide the aforesaid circuitry which is comprised mainly of such transistors as are easily manufactured with semiconductor integrated circuits, while reducing the number of resistors which are difficult to make with semiconductor integrated circuits, so that said circuitry is suitable for being made with semiconductor integrated circuits.

The foregoing as well as the other objects, features and attendant advantages will be understood more clearly by reading the following detailed description when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram, showing an example of the conventional sustain keyer circuitry for use in an electronic musical instrument;

FIG. 2 is a circuit diagram, showing a sustain keyer circuitry provided with a sustain time control circuit and representing one embodiment of the invention;

FIG. 3 is a graph, illustrating the conducting to nonconducting level ratio of the circuitry of FIG. 2;

FIG. 4 is a circuit diagram of a sustain keyer circuitry according to another embodiment of the invention;

FIGS. 5 and 6 are circuit diagrams, showing modifications, respectively, of the circuitry of FIG. 4;

FIG. 7 is a graph, showing the conducting to nonconducting time ratio of the circuitries of FIGS. 4 to 6;

FIG. 8 is a circuit diagram of a sustain keyer circuitry according to still another embodiment of the invention;

FIGS. 9 and 10 are circuit diagrams, showing modifications, respectively, of the circuitry of FIG. 8;

FIG. II is a circuit diagram, showing a sustain time control circuit according to another embodiment of the present invention;

FIGS. 12 and 13 are diagrams, illustrating the functions of the circuitries shown in FIGS. 11 and 2, respectively;

FIG. 14 is a circuit diagram of a sustain time control circuit according to still another embodiment of the present invention; and

FIG. 15 is a circuit diagram of a sustain time control circuit according to yet another embodiment of the invention.

In the drawings, like parts are indicated by like symbols and reference numerals.

l DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will hereunder be described in detail with respect to an embodiment shown in FIG. 2.

The circuit arrangement embodying the present invention is such, (as shown within the block indicated by a-dot-and-adash line in FIG. 2,) that there are used first and second field effect transistors, FET Q, and FET Q which are connected in series so as to be able to be operative from both DC and AC viewpoints, and the source electrode of the first FET Q, is grounded, whereas a tone signal is applied to the gate electrode thereof through an input terminal T,, the drain electrode thereof being connected to the source electrode of the second FET Q which is the other of the two, the drain electrode of this second FET Q being connected to a power source -V,,

via a load resistance element R, there being interposed a serial circuit consisting of a resistance element R and a keyoperated switch 8,, between the gate electrode of said second FET Q and said power source V,, to thereby form a sustain keyer circuit SA so as to derive said tone signal at the output terminal T from the drain electrode of said second FET Q through a capacitor C by the keying operation of said keyoperated switch 8,. Furthermore, the gate electrode of said second FET Q, is connected to the power source -V,, via a capacitor C,,. Also, this gate electrode of the second FET O is connected to the drain electrode of a third FET 0 having its source electrode grounded, and the gate electrode of this third FET 0;, is connected to a slidable contact r,, of a variable resistor R, which, in turn, is interposed between said power source V,, and the ground, to thereby form a sustain time control circuit. In FIG. 2, the symbols C and 0 represent a capacitor for determining the sustain time and another FET having its source electrode grounded and being used as a resistance element, respectively. Furthermore, the sustain keyer circuit SA given in the block indicated by a-dot-and-a-dash line and said FET 0;, are provided for example, in a console of the electronic musical instrument each in a number, for example, of 90-100 which is the number of tone generators'provided in accordance with the number of the keys of the keyboard of the electronic musical instrument. Whereas, there is used only one variable resistor (potentiometer) R which is assigned for determining the resistance value between the drain and source electrodes of the FET 0 by adjusting the gate potential of this FET Q said variable resistor R, being arranged so that its slidable contact r,, is used in common to the respective gate electrodes of the multiplicit number of FET Q whereby, by operating the aforesaid variable resistor R,,, the sustain time of the output signal at the opening of the key-operated switch S may be adjusted to a desired time via the FET Q The sustain keyer circuit of the present invention which contains therein the sustain time control circuit is of the foregoing arrangement. Description will hereunder be made on the actions of this circuitry. The player or the user of the electronic musical instrument may key the key-operated switch S, which is adapted to close in association with the depression of the selected keys of the keyboard of this instrument performed by the player. The resistance elements R and R, as well as the power source V,, are preliminarily arranged so that these resistance elements will have values and the power source will have a voltage value such that both the FET Q and the FET Q will be rendered to the cutoff state or to the on" state upon said keying operation of the player. Also, arrangement is provided so that, when the key-operated switch S is closed, the transient characteristics in the course of the starting of conduction of both the FET Q and FET Q are to be determined by the time constant which, in turn, is determined by the capacitance of the capacitor C, and the resistance element R which are interposed in the gate circuit of the FET O to thereby determine the buildup characteristic of the signal detected at the output terminal T Whereas, when I the key-operated switch S is opened, the transient characteristics in the course of the ending of conduction of both the FET Q, and the FET Q are to be determined by the time constant which, in turn, is determined by such factors as the capacitance of the aforesaid capacitor C, and the resistance value between the drain and source electrodes of the FET O to obtain a desired decay characteristic (meaning the socalled sustain time) of the aforesaid signal detected. Furthermore, a tone signal having a predetermined frequency and a predetermined waveform obtained from a separately installed tone generator (which includes flip-flop circuits, but any known devices will be usable, and therefore, it is not shown in the drawing) is always applied to the input terminal T.. In case the FET O is rendered to its on" state while retaining its predetermined inner resistance value by adjusting the position of the slidable contact r, of the variable resistor R it should be noted that, when the key-operated switch S, is open, the juncture between the drain of the FET Q and the gate of the FET O in each set, is at the ground potential. Therefore, there is applied to this gate of the FET 0, no negative voltage which would render the FET O to the on state, with the result that this FET Q, is in its cutoff state. Also, there is applied no negative voltage to the drain electrode of the FET O, which is connected to the source electrode of said FET Q2, and accordingly, this FET Q is also in its cutoff state. After all, both of the two FETs, Q and 0:, which are connected in series to each other are retained in their shutoff state, so that the leakage current (dark current) between the drain electrode and the source electrode between these two FET's is minimal, being in the order of IO ampere (l nano-ampere). Also, the static capacity between the drain electrode and the source electrode between these two FETs is likewise markedly small as compared with that of the ordinary transistors. Besides, these two FETs are connected in series from both the AC and DC viewpoints, and accordingly, the aforesaid capacity is reduced to approximately one-half. Thus, the tone signal which is always applied to the gate side of the FET Q, will hardly be produced at the drain side of the FET 0 As a result, there can be obtained a conducting to nonconducting level ratio of the signal (or the signal to noise ratio) which is at least db. as will be noted from the actually measured value as indicated by the dot-dash curve a in FIG. 3.

It is to be noted that, in the foregoing operation, the capacitor C which is connected to the gate circuit of the FET Q, is in the state of being charged up with the voltage of the power source V through the third FET 0;, having a considerably high drain-source resistance.

On the other hand, when said key-operated switch S is closed, the charge on the capacitor C, which has been in the charged-up state in the foregoing stage is discharged through the resistance element R, which is connected in series to this key-operated switch S and also, the potential of the juncture between the gate electrode of the FET Q and the drain electrode of the FET Q approaches the potential of the power source V,,. As a result, first, the FET 0 will be rendered to the conductive state, and then almost simultaneously therewith the FET Q will be rendered to the conductive state. Accordingly, the tone signal which is being applied to the gate electrode of this FET Q, is detected at the output terminal T via the drain electrode of this first FET Q and the source and drain electrodes of the second FET Q2 successively in this order. This detected tone signal is then amplified, for example, and thus, it is possible for one to obtain an audible sound wave converted from said tone signal and given out through a loudspeaker or like appliances.

Next, when the key-operated switch S, is opened again, the capacitor C which has been in the discharged state in the foregoing stage begins to be charged up with the voltage of the power source V via a considerably high predetermined inner resistance between the drain-source circuits of the FET 0 Also, the potential of the juncture between the gate of the FET Q and the drain of the FET Q approaches the ground potential. Along with this, when the potential of each of the plurality of juncture rises above (meaning more positive than) a predetermined potential, the FET Q will be rendered to its nonconductive state before the other, and then, almost simultaneously with this, the FET Q, will also be rendered to its nonconductive state. Thus, both of the two FETs will be rendered to the nonconductive state as in the case of the opened state of the key-operated switch 8,. Accordingly, the tone signal which is being applied to the input tenninal T is substantially completely shut off by these FETs at the end of the lapse of a sustain time which is determined by a time constant which, in turn, is determined by the capacitance of the capacitor C, and the inner resistance of the FET 0,. As a result, the signal ceases to be detected at the output terminal T, At such a time, the conducting to nonconducting level ratio of the signal which is produced at the output terminal T at the aforesaid time of signal detection may be obtained at a high level such as 90 db. or more as shown by the actually measured value which is indicated by the dot-dash line in FIG. 3. Thus, it is possible to improve this level ratio by as much as about 40 db. as compared with the low values of 50-55 db. obtained with the conventional circuitries. Furthermore, in view of the fact that the resistance value between the drain and source electrodes of the FET Q, will increase as, for example, the slidable contact r, of the variable resistor R, is brought closer to the ground side. As a result, the transient time in the course of charge-up of the capacitor C,, i.e., the sustain time of the electronic musical instrument, will become prolonged. Contrariwise, as the slidable contact r, is brought closer to the power source V, side, the resistance value between the drain and source electrodes of the FET Q will decrease, so that the sustain time will become shortened.

As stated above, according to this instant embodiment, the two FETs which are connected in series to each other from both the DC and AC viewpoints are rendered simultaneously to either the conductive state or the nonconductive state via the key-operated switch 8,, so that the output signal which is detected via the serial circuit of these two FETs can be positively keyed or switched-over between on and off. Thus, it is possible to substantially improve the conducting to nonconducting level ratio of the signal as compared with the circuitry utilizing only one transistor of the ordinary type as shown in FIG. 1. Furthermore, since according to the present invention there are used field effect transistors in the sustain keyer circuit SA, the whole system will operate sufficiently even when a tone signal of a considerably large amplitude (such as the order of 10 V,, or more) is directly applied to the gate circuit of the FET Q and in addition, the input impedance which is as high as several hundred k0. may be easily obtained without paying any particular consideration such as the additional provision of a compensatory impedance. Thus, adverse effects such as an electric loss or a distortion of waveform can be altogether eliminated. Besides, in the instant embodiment, his only necessary to provide no particular additional elements but only two FETs and resistance elements R and R, in the sustain keyer circuit SA. Therefore, it is possible to eliminate the necessity for the use of a large number of resistors and a capacitor of a large capacity as is required in the prior art described above. This makes it extremely easy to effect integration of the sustain keyer circuitries in electronic musical instruments of the type described. Thus, the present invention is of a superior advantage of positively accelerating the tendency of making electronic musical instruments into compact size, which provides for a great merit industrially. Description has been made on an instance in which the control of the sustain effect according to the present invention is effected by both the capacitor C, and the FET It will be understood easily that this control may be performed by the application of a system of other type.

In the control of the sustain effect according to this instant embodiment, the transient characteristics in the courses of both beginning of conduction and of ending of conduction of the switching elements of such field effect transistors as FET Q, and FET Q, with which the tone signal in an electronic musical instrument is to be keyed are determined, respectively, so that the charge-up and/or the discharge transient phenomena of the capacitor C, for determining the buildup and decay characteristics of the tone signal of the electronic musical instrument are caused to develop, respectively, through the resistance element R, which is connected in parallel with said capacitor C, and separately through the third FET Q, having a high inner impedance and being connected in series to said capacitor C, and via the key-operated switch S, which is adapted to close upon the depression of any selected keys of the keyboard of the electronic musical instrument. Along with this, the decay characteristic of the tone signal i.e., the sustain time characteristic of the electronic musical instrument can be controlled by first altering the inner resistance value between the drain and source electrodes of said F ET Q and whereby altering the transient characteristic of the capacitor C, in the course of its charging-up. Accordingly, even when the capacitance of the capacitor C, used is set to have a small value (for example, 0.1-0.5 microfarad), it is still sufirciently possible to obtain a sufi'iciently prolonged sustain time by causing the envelope of the waveforms during the charge-up time to follow a gradual down-going pattern. Thus, as compared with the high capacitance, such as [00 microfarads, of the capacitor C assigned for determining the sustain time used in conventional electronic musical instruments, the capacitor C, which is used in the instant embodiment may be of a capacitance as low as 1/500 of that of the capacitors in the conventional instruments. Accordingly it is possible to use capacitors of other types than electrolytic capacitors, that is to say, it is possible to employ paper capacitors or metallized paper capacitors of compact size. As a result, it is possible to minimize the variation of the static capacitance of the capacitor, and accordingly, to minimize the variation of the sustain time in the electronic musical instrument. in view of the fact also that the input impedances of the gate electrodes of the aforesaid FETs, 0, through Q3, are markedly high, the variable resistor R, for example, according to this embodiment, for altering the gate potential of the FET Q assigned for determining the charge-up time of the capacitor C is such that, by the provision of a single variable resistor 11,, it can alter the gate potentials of a large number of FETs accurately and stably, and thereby uniformly and simultaneously determine the sustain time of the electronic musical instrument. This not only will make it possible to reduce the number of such variable resistors used as compared with the conventional circuitries, but also will make it easy to integrate the circuitries since it is sufficient to use only two resistance elements in the circuitry according to this embodiment. As a result, it becomes possible to positively accelerate the reducing of the size of the electronic musical instruments. Besides, the aforesaid capacitor C, may employ a paper capacitor or a metallized paper capacitor having a capacitance of the order ranging from 0.1 to 0.5 microfarad as stated above. Thus, there are a number of advantages such that the circuitry is produced in a markedly compact size and light in weight and at a low cost as compared with those utilizing electrolytic capacitors of a large capacity, so that this embodiment is of a great industrial value.

Description has been made on an instance in which the capacitor C, is connected between the gate electrode and the power source V, of the FET 0,. In this instance, the variation of the gate potential of this FET 0 resulting from the keying operation of the key-operated switch S, is exactly the same in fashion as that described above. However, the chargeup to discharging relative relation of the capacitor C, will be the reverse of the relation described above. It should be understood also that, in the FET Q and FET 0, according to this embodiment for keying the tone signal may employ switching elements of other types such as three-pole diodes, drift-type transistors, alloy-diffused transistors, and microalloy diffused transistors. Also, in this embodiment, description has been made on the instance in which two field effect transistors which are connected in series to each other are used. It should be understood easily that more than two switching elements, such as the field effect transistors, may be used by connecting them in series to effect the cutting-off and conducting switching of the tone signal. I

Description will hereunder be made in detail on the embodiment shown in FIG. 4. The circuit arrangement embodying the invention is such, as shown in the block defined by the chain line in FIG. 4, that, of the three FET'S, Q, Q and Q the source electrode of one, FET 0, of them is grounded, and that a tone signal coming through an input terminal T, is applied to the gate electrode thereof, and that the drain electrode thereof is connected to the source electrode of another FET Q via the drain and sourceelectrodes of the other FET 0, and that the drain electrode of said FET Q is connected to a power source V, via a load resistance element R, whereas the gate electrode of this FET Q is connected in common to the gate electrode of the FET Q and that a serial circuit consisting of a resistance element R, and a keyoperated switch S, is interposed between the juncture of said common gate circuit and the power source V,, to thereby form a sustain keyer circuit SB so as to derive the tone signal from the drain of the FET O and via said capacitor C and an output terminal T upon the keying operation of said keyoperated switch 8,.

It should be understood that said manner of connection of the gate circuits of the FET Q and the FET O in the aforesaid arrangement may be altered to the manner in which, as shown in FIG. 5, the gate circuit of the FET Q is connected in common to the gate circuit of the FET Q by substituting the FET O by a FET Q to form a sustain keyer circuit SB so that the tone signal applied to the gate electrode of the FET Q may be derived at the output terminal T via the drain circuit of the FET Q upon the keying operation of the key-operated switch 8,.

It should be understood that the capacitor C, and the FET 0, shown in FIGS. 4 and 5 represent a capacitor for determining the sustain time and another FET having its source electrode grounded and being used as a resistance element, respectively, and also that the sustain keyer circuits SB and SB which are given within the blocks defined by the chain lines and said FET Q, are to be provided in, for example, a console of an electronic musical instrument in a number corresponding to the number, for example, 90-100, of the tone generators which are provided in accordance with the keys of the keyboard of the electronic musical instrument. It should be understood further that the variable resistor R, for adjusting the gate potential of the FET Q, and whereby for determining the resistance value between the drain and source electrodes thereof is used only one in number in such a way that its slidable contact r, is connected in common to the large number of gate circuits of the respective FET Q,s which are used as the variable resistance elements of a correspondingly large number.

The circuit arrangement according to the instant embodiment for an electronic musical instrument is as described above. Description will hereunder be directed to the actions of this circuitry with respect to the embodiment shown in FIG. 4. The resistance elements R and R, and the power source V, are set beforehand so that, upon the keying operation, by the player or the user of the electronic musical instrument, of the key-operated switch S, which is adapted to close in association with the depression applied to any selected keys of the keyboard during the playing, these resistors and the power source will assume such values as will render the FETs, 0,, through Q to either the cutoff" state or the on state, respectively. Also, the transient characteristics in the course of the beginning of conduction of the FETs, Q through 0, are arranged to be determined, when the key-operated switch S, is closed, by the time constant which, in turn, is determined by the capacitance of the capacitor C, and the resistance element R, which are interposed in the gate circuits of the FET O and the FET Q, (meaning between the juncture g and the power source -V,), to thereby determine the buildup characteristic of the tone signal detected at the output terminal T whereas, when the key-operated switch S, is opened, the transient characteristics in the course of the ending of conduction of the FET Q FET 0,, are determined by the time constant which, in turn, is determined by such factors as the capacitance of the capacitor C, and the drain-source resistance value of the FET 0,, to thereby render the decay characteristic (so-called sustain time) of said detected signal to a desired characteristic. Furthermore, a tone signal having a predetermined frequency and a predetermined waveform and coming from a separately installed tone generator (which may be comprised of flip-flop circuits, but any known tone generator may be used, so that this is not shown in the drawings) is applied always to the input terminal T..

In the case where the FET Q, is rendered to the on" state while retaining its predetermined inner resistance value by adjusting the position of the slidable contact r, of the variable resistor R,, it is to be noted that in case the key-operated switch S, is open, the juncture between the drain electrode of the FET Q, and the gate electrodes of both the FET Q and FET Q12 in each set is at the ground potential. Accordingly, there is applied to these gate circuits no negative voltage which would render the FET On and the FET Q12 to the on" state, with the result that these FETs are held in their cutoff" state. Also, the other FET 0,, which is connected to the source electrode of the FET Q is rendered to the cutoff" state because there is applied no negative voltage to the drain electrode of this FET 0 After all, all of the three FETs, Q through 0, which are connected in series are held in their shut-off state, and accordingly, the leakage current (dark current) between the drain and source circuits of these FETs is minimal, being of the order of 10 (l nano-ampere), and also, the static capacity between the drain and the source circuits of these FETs is markedly small as compared with that obtained in ordinary transistors. Besides, in view of the fact that these three FETs are connected in series from both AC and DC viewpoints, the aforesaid capacity will reduce to approximately 6. Therefore, the tone signal which is always applied to the gate circuit of either the FET Q or FET Q (see FIG. 5) will hardly be produced at the drain side of the FET Q As a result, the switching ratio (signal conducting to nonconducting ratio or S/N ratio) may be obtained at a large level as I00 db. or more as shown by the actually measured value which is indicated by the solid line b in FIG. 7.

On the other hand, when the key-operated switch S, is closed, the charge on the capacitor C, which has been in the charged-up state in the aforesaid stage by the resistance element R, which is connected in series to this key-operated switch S, is discharged, and along with this, the potential of the juncture g between the gate circuits of both the FET Q and the FET 0, and the drain circuit of the FET 0, approaches the potential of the power source V,. As a result, both the FET Q and the FET O are first rendered to the on state, and then, almost simultaneously therewith, the FET Q will also be rendered to the on state, so that the tone signal which is applied to the gate circuit of this FET Q is detected at the output terminal T via the drain circuit of said FET 0, and via the source and drain circuits of the FET 0, and the FET Q respectively, in this order. By, for example, amplifying this detected tone signal, it is possible to obtain auditory sound wave of the converted tone signal through a speaker or like appliances.

When the key-operated switch S, is opened again, the capacitor C, which has been in the discharged state in the aforesaid stage begins to be charged up with the voltage of the power source -V, via the FET 0,, and also the potential of the juncture g between the gate circuits of the FET Q and the FET On and the drain circuit of the FET Q approaches the ground potential. When the potential in each set rises above (meaning more positive than) a predetermined potential, both the FET Q 1 and the FET 0 are rendered to the cutoff state first of all, and then almost simultaneously therewith, the FET O will also be rendered to the cutoW state, with the result that these three FETs will be rendered to the shut-off state, respectively, as in the preceding case where the keyoperated switch S, is opened. Accordingly, the tone signal which is applied to the input terminal T, is almost completely shut off by these FETs after the lapse of a sustain time which is determined by the time constant which, in turn, is determined by the capacitance of the capacitor C, and the inner resistance value of the FET 0,, so that the tone signal is no longer detected at the output terminal T In this case, the output signal switching ratio (signal level ratio) which is derived at the output terminal T at the aforesaid time of detection of the tone signal may be obtained in such a high level as I db. or more as shown by the solid line b in FIG. 7. Thus, it is possible to improve the value of this ratio by about db. as compared with that obtained from other circuitry shown in FIG. 2.

It should be noted that, in case the connection shown in FIG. 4 of the gate circuits of both the FET Q and the FET Q is replaced in the manner as shown in FIG. 5, it is likewise possible to obtain a high level, such as 100 db. or more as shown by the solid line b in FIG. 7, of output signal switching ratio with which the tone signal applied to the gate circuit of the FET 0, via the input terminal T is to be derived from the drain circuit of the FET Q In this case, however, the source circuit of the FET 0, is cut off from the ground owing to the cutting-off of the respective FETs, especially owing to the cutting-off of the FET Q and accordingly, no effective input signal becomes to be applied to the gate-source circuit of this FET Q so that the signal switching ratio is considered to be improved.

With respect to the arrangement of sustain keyer circuit SC shown in FIG. 6 in which five FETs, Q are connected in series, so that an input signal is applied to the gate circuit of one, meaning FET Q of these five FETs and that the output signal is adapted to be derived from the drain circuit of the FET Q the signal switching ratio can be improved further to the order of l lO-l db. as shown by the dotted line c in FIG. 7.

As described above, according to this embodiment, three or more FET's which are connected in series can be rendered simultaneously to either the on" state or the cutoff state via the key-operated switch 5,, and the output signal which is detected after being passed through the serial circuits of these FETs can be positively keyed. As a result, it is possible to improve the signal switching ratio by l0-2O db. as compared with the circuitry of this type shown in FIG. 2 in which only two FET's are used. Also, even when there arises a drop of insulation or short-circuiting in the respective FETs, it is still possible to positively retain a sufficiently large signal switching ratio. Thus, the instant embodiment is able to greatly improve the safety of the sustain keyer circuit which constitutes the principal section of an electronic musical instrument. It should be noted further that, in circuitries of this type, an increase in the number of FETs will never hamper the integration of the circuitries and that, even where there is some increase in the area occupied by these FETs, such an inconvenience may be overcome to a great extent by many superior advantages such that a safety operation can be insured, and thus, this embodiment is of a great industrial merit.

Description has been made on the instance in which the control of the sustain effect is effected by the capacitor C, and the FET 0,. It should be apparent that this controlling may be effected by the use of systems of other types.

Description will hereunder be made on some other embodiments of the sustain keyer circuit shown in FIGS. 8 through 10. This circuit employs pairs of FETs which are connected in parallel to the FET's, respectively, which are used as the switching elements in the circuits shown in FIGS. 4 to 6 which represent the preceding embodiments of the invention. The instant embodiments are insured for positive and safe operation of the circuitries even when there arises a drop of insulation and a short-circuiting or opening of circuit in each of the FETs. Accordingly, the instant embodiments are of essentially the same arrangement with that of said preceding embodiments, and the actions of the circuitries are substantially the same also, so that their detailed explanation is omitted.

Next, description will be directed to still another embodiment in which three FETs are used in place of one FET in the sustain control circuit shown in FIG. 2, by referring to FIG. I I

First, in FIG. 2, when the key-operated switch S, is opened again at the time t, in FIG. 13, the capacitor C, which has been in the discharged state in the aforesaid preceding stage begins to be charged up with the voltage of the power source V via a relatively large predetermined inner resistance between the drain-source circuits of the FET Q, and the potential of the juncture between the gate circuit of the FET Q and the drain circuit of the FET Q, approaches the ground potential. Also, when the potential of this juncture in each set rises above (meaning more positive than) a predetermined potential at the time t, or I; in FIG. I3, the FET O is rendered to the "cutof state first of all, and then, almost simultaneously therewith, the FET Q, is also rendered to the "cutoff state, so that these two FETs are rendered to the shutoff state as in the case in which the aforesaid key-operated switch S, is in the opened state. Thus, the tone signal which is applied to the input terminal T, is almost completely shut off by these FETs at the end of lapse of the sustain time which is determined by the time constant which, in turn, is determined by the capacitance of the capacitor C, and the inner resistance of the FET 0,. Accordingly, there will no longer be detected a signal at the output terminal T In view of the fact that the resistance value between the drain and source circuit of the FBI 0: increases as, for example, the variable voltage source represented by contact r, is brought closer toward the ground potential zero, the transient length of time of charging up of the capacitor C,, i.e., the sustain time of the electronic musical instrument, is prolonged to the length of time from t, to 1 as shown by the chain line in FIG. 13. Contrariwise, as r, approaches closer toward the negative voltage of the other power source V,, the resistance value between the drainsource circuits of the FET 0;, reduces so that the sustain time will accordingly decrease to the length of time from t, to r, in FIG. 13. Accordingly, it is possible to control, with a relative easiness, the sustain time of an electronic musical instrument. In the embodiment shown in FIG. 2, however, owing to the nonrectilinear characteristic of the FET Q;,, the decay characteristic of the tone signal within said sustain time will show an upwardly convexed curve as shown by the envelope curve in FIG. 13, which gives an unnatural ending of the audible sound during the decay thereof in an electronic musical instrument, and therefore, this is not desirable. It is, therefore, the object of this instant embodiment to solve the foregoing inconvenience and drawback. This embodiment will hereunder be described in detail by referring to FIG. 11. It should be understood that the portion given in the block defined by the chain line in FIG. 11 represents a sustain keyer circuit SA which is arranged in the same manner as the sustain keyer circuit SA given in the block defined by the chain line in FIG. 2. The gate circuit of the FET Q given in this block is grounded via the drain electrode and the source electrode of the serially arranged FET Q and FET 0,, respectively, in this order, and also said gate circuit of the FET Q is connected to the gate circuit of the FET Q The gate circuit of this FET O is connected to the drain circuit of another FET 0, having its source electrode grounded. The gate circuit of this latter FET Q, is connected to a fixed bias power source V, which is of a voltage somewhat lower than that of the supply power source V, of the aforesaid sustain keyer circuit SA. Furthermore, the gate circuit of said FET O is connected to a variable voltage source -V,.

It should be understood that the sustain keyer circuit SA given in the block defined by the chain line in FIG. 11 and said FETs, O to 0 are provided, respectively, in, for example, a console of an electronic musical instrument and in a number corresponding to the large number of tone generators which are provided in accordance with the number of the keys of the keyboard of the electronic musical instrument. Whereas, the power sources -V, V and V are provided only one each so as to be connected in common to the large number of sustain keyer circuits and the correspondingly large number of FET'S, O3 to Q5.

Description will hereunder be made on the action of the sustain time control circuit of this embodiment. In case the power sources V, and V, are set to have predetermined voltages and in case said FET Q FET 0 have predetermined values of impedance between the drain-source circuits,

respectively, the junction between the drain circuit of the FET and the gate circuit of the FET O is at the ground potential in each set. Accordingly, there is applied to this gate circuit no negative voltage which would render the FET O to the on" state, so that this FET O is in its cutoff state. Also, the FET which is connected to the source circuit of said FET O is in its cutoff" state because there is applied no negative voltage to the drain circuit of this FET 0,. After all, these two FET Q, and FET O, which are connected in series are held in their shutoff state. As a result, the tone signal which is applied always to the gate circuit of this FET Q will not produce on the drain side of the FET Q It should be understood that the capacitor C which is connected to the gate circuit of the FET Q, is in the state of being charged up with the voltage of the power source -V via the predetermined inner resistances between the drain-source circuits of the other FETs, Q Q and 0 On the other hand, when the key-operated switch S, is closed, the charge on the capacitor C which, in the aforesaid stage, has been charged up is discharged through the resistance element R, which is connected in series to said keyoperated switch S and also, the potential of the juncture between the gate circuit of the FET Q and the drain circuit of the FET Q approaches the negative potential of the power source V, As a result, the FET Q, will be rendered to the conductive state first of all, and then, almost simultaneously therewith, the FET Q will also be rendered to the conductive state. As a result, the tone signal which is being applied to the gate circuit of this FET Q is detected at the output terminal T via the drain circuit of said FET Q and the source and drain circuits of the FET Q successively in this order. By, for example, amplifying this detected signal, it is possible to obtain, through a speaker or like appliances, an audible sound wave having been converted from the tone signal.

Next, when the key-operated switch S is opened again at the time t shown in FIG. 12, the capacitor C, which has been in the discharged state in the preceding stage begins to be charged up with the voltage of the power source V,,, via the predetermined inner resistances between the respective drain and source circuit of the FETS, Q Q and the gate potential of the FET Q and the drain potentials of the FET Q and FET Q approach the ground potential, respectively. When these potentials rise above (meaning more positive than) a predetermined potential at the time t, or shown in FIG. 12, the FET Q and the FET Q, are both rendered nonconductive. Thus, these two FETs are shut off in the same manner as described in connection with the instance where the key-operated switch S, is in the opened state. As a result, the tone signal which is being applied to the input terminal T is shut off by these two FETs, Q and Q at the end of a lapse of the sustain time (t or which is determined by the time constant which, in turn, is determined by the capacitance of the capacitor C o and the respective apparent drain-source resistances of the FETs, 0 -0 and FET 0,. Thus, there is no longer detected the tone signal at the output terminal T It should be understood that the aforesaid sustain time is such that a desired sustain effect may be obtained by varying the DC potential of the gate circuit of the FET Q resulting from the adjusting of the voltage of the variable voltage source V,. In view of the fact, however, that, in such a case, the drain-source resistance value of the FET Q, will increase as, for example, the aforesaid voltage of the voltage source -V, approaches closer toward the ground potential zero, the

transient current-during the charging-up of the capacitor voltage of the fixed voltage source -V,,,, the drain-source resistance value of the FET 0 will decrease. Accordingly, the limitation which has been imposed on the transient current during the charging-up of the capacitor C,,which flows via the drain-source resistance of the FET O; which is connected in series to said FET Q, is lightened so that the duration of the transient time during the charging up of the capacitor C, is reduced. As a result, the sustain time of the tone signal will become shortened to the length of time from 2,, to t, as indicated by the solid straight line in FIG. 12. Thus, it is possible to control the sustain time of the electronic musical instrument by altering the gate potential of the FET 0.. It should be noted that, especially in this instant embodiment, the transient time during the charging-up of the capacitor C, assigned for determining the sustain time is controlled via the serial drainsource circuit of the FET 0., which is used as the main variable resistance element and the similar circuit of the FET 0 which serves as the variable resistance load for correcting the nonrectilinear voltage to current characteristic of said FET Q and also that the current flowing through said FET O is controlled in such a manner as will correct the nonrectilinear voltage to current characteristic of the FET O, which is used as the main variable resistance element, via the FET 0,, which is connected in parallel to the gate circuit of the FET Q and also to the ground, and further that, whereby the decay characteristic of the tone signal within the aforesaid sustain time can be rendered rectilinear as shown by the straight envelope line in FIG. 12. Thus, it is possible to obtain the optimum acoustic exponential decay curve.

As stated above, according to this instant embodiment, the current for charging up the capacitor C, assigned for determining the sustain time of an electronic musical instrument is controlled via the drain-source circuits of the FET O, which performs rectilinear action and of the FET O; which serves as the load of said FET Q. successively in this order to thereby increase or decrease the transient time during the charging up of said capacitor C whereby, it is possible to control the sustain time of the electronic musical instrument as desired, and also it is possible to obtain the envelope curve of the sustain time always in the form of the optimum exponential decay curve regardless of themanner of this control. Therefore, according to this embodiment, it is possible to completely eliminate the unnaturalness of the decay pattern of the tone signal which would be encountered to some extent in such circuitries of this type as the one shown in FIG. 2. Thus, the instant embodiment may be most desirably applied to the sustain time control unit of electronic musical instruments. Also, in view of the fact that the sustain time control system may be obtained without the provision of any additional resistance elements in the circuitry of the instant embodiment, the latter embodiment is of a number of superior advantages such that the integration of the circuitries can be attained easily, in addition to the foregoing advantage. Thus, this embodiment is of a great industrial value.

In the aforesaid embodiment, description has been made on the instance in which the capacitor C is connected between the gate circuit of the FET Q and the power source V, It should be understood, however, that this capacitor C, may instead be connected between the gate circuit of the FET Q and the ground point. In such an instance, the variation of the gate potential of the FET Q resulting from the keying operation of the key-operated switch S, is effected in the same way as in the aforesaid embodiment, but the relation between charging up and discharging of the capacitor C, will be the reverse of that of said embodiment.

Next, description will be made on still another embodiment, shown in FIG. 14, of the sustain time control circuit. This is an improvement of the embodiment shown in FIG. 11. More specifically, in the embodiment shown in FIG. 11, there is the necessity for additional provision of a DC source separately from the main power source -V, in view of the need for a fixed voltage source V,, for biasing the gate circuit of the FET Q To this end, there will be portions in the circuitry in which are employed various electric parts such as a bleeder resistor and a decoupling capacitor. This will inevitably lead to an increase in the size of the aforesaid particular portions of the power source circuits as a whole and will accordingly lead to an increase in the cost of the system as a whole. Furthermore, there will be required a number of lead wires for use in the connection of said voltage source V,,, to said FET since this FET has to be provided in a number which is approximately 90-l00 in one electronic musical instrument as stated previously. This will lower the efficiency in the fabricating operation of the circuitries and will greatly hamper the mass productivity of electronic musical instruments. Thus, the embodiment shown in FIG. 11 has a number of drawbacks. To eliminate these drawbacks, the embodiment shown in FIG. 14 provides the following arrangement. That is to say, in place of FET Q the gate circuit of the FET Q, is connected to the fixed voltage source V,, which, in turn, is connected to the sustain keyer circuit SA, and also the source circuit of said FET O is connected in common to the source circuit of the FET Q Accordingly, this FET Q, does not require a separate gate-biasing voltage source, and yet it is possible to effect correction of the action of this FET so as to have a desired rectilinear characteristic as described in connection with FIG. 12.

Next, description will be directed to yet another embodiment of the sustain time control circuit by referring to FIG. 15. Like the embodiment shown in FIG. 14, the instant circuitry in FIG. 15 shows an arrangement with the omission of one power source assigned for biasing the FET in FIG. 11. More specifically, the difference of this instant embodiment from the circuitry shown in FIG. 11 lies in the following arrangement. The FET O is connected in series to another FET Q whereas the gate circuit of said FET Q is connected in common to the gate circuit of the aforesaid FET Q4, and this common gate circuit is connected to a variable voltage source V Also, the gate circuit of the FET Q, is connected to a fixed voltage source V,, which, in turn, is connected to the aforesaid sustain keyer circuit SA. In this circuit arrangement, the sustain time is such that a desired sustain effect like the one described in connection with FIG. 12 can be obtained by adjusting the voltage of the variable voltage source V, and whereby altering the gate DC levels of both the FET Q and FET Q simultaneously and in the same direction.

Furthermore, it is possible, in this embodiment, to omit the fixed power source -V,, for biasing the FET Q which is assigned for correcting the action of the FET Q into rectilinear characteristic. Accordingly, this will altogether eliminate the use of a number of lead wires (not shown) which would otherwise have to be provided between the circuits of this type and the bias voltage source. As a consequence, the workability of the manufacture of electronic musical instruments having circuitries of this type will greatly improve to become suitable for mass production of such instruments. Also, the fact that no provision of additional resistance elements is necessary will permit an easy integration of the circuitries.

I claim: 1. In an electronic musical instrument, a sustain keying circuit comprising:

an input terminal for receiving an input tone signal from a tone generator,

an output terminal for providing a keyed output tone signal having desirable sustain characteristics,

first and second active elements, each having first and second electrodes and a control electrode for controlling current flow between said first and second electrodes,

said first electrode of said first active element being connected to said second electrode of said second active element, of said first and second active elements being electrically connected together in series and this series arrangement also being connected in series with a load resistor and a power source,

said control electrode of said first active element being electrically connected to said input terminal,

said load resistor being electrically connected to said output terminal, and

keying means including a key-operated switch connected to the control electrode of said second active element, said means producing a controlled tone buildup and a decay sustain characteristic which is produced after key activation and deactivation respectively while yet severely limiting undesirable tone feed through to the output terminal under quiescent circuit conditions.

2. A sustain keying circuit as in claim I wherein said keying means includes a capacitor connected between the control electrode of said second active element and an AC ground.

3. A sustain keying circuit as in claim 2 wherein said keying means further includes:

a third active element having first and second electrodes and a control electrode,

said first electrode of said third active element being connected to said control electrode of said second active element,

said second electrode of said third active element being electrically connected to one terminal of said power source, and

said control electrode of said third active element being connectable to a source of variable voltage whereby the sustain characteristics of said keying circuit may be varied as desired by varying said variable voltage.

4. A sustain keying circuit as in claim 1 further comprising:

a third active element having first and second electrodes and a control electrode, said first and second electrodes of the third active element being electrically connected in series with the first and second electrodes of the first and second active elements, and I the control electrode of said third active element being connected in common with the control electrode of the second active element whereby even less undesirable tone feed through is produced while also increasing the reliability of the keying circuit.

5. A sustain keying circuit as in claim 1 wherein each of said first, second and third active elements is provided with another active element connected in parallel therewith via electrical connections between respectively similar electrodes of each resulting pair of active elements.

6. A sustain keying circuit as in claim 3 further comprising:

fourth and fifth active elements each having first and second electrodes and a control electrode,

said first and second electrodes of said fourth active element being connected in series with the first and second I electrodes of said third active element,

the control electrode and the first electrode of said fourth active element being connected together to cause the fourth active element to serve as a variable resistance for correcting nonlinearities in the sustain characteristics of said keying circuit, and wherein the first and second electrodes of said fifth active element are connected from said control electrode of the fourth active element to groud with the control electrode of the fifth active element connectable to a power source whereby the characteristic decay envelope of the keyed output is exponentially shaped.

7. A sustain keying circuit as in claim 3 further comprising:

fourth and fifth active elements, each having first and second electrodes and a control electrode,

said first and second electrodes of said fourth active element being connected in series with the first and second electrodes of said third active element with the control electrode and the first electrode of said fourth active element being connected together to cause the fourth active element to serve as a variable resistance for correcting nonlinearities in the sustain characteristics of said keying circuit, and wherein the first and second electrodes of said fifth active element are connected to the first and second electrodes respec- 7 17 18 tively of the fourth active element with the control elec- I the second electrode of said fifth active element being controde of the fifth active element connectable to said nected to the first electrode of said sixth active element, power source in common with said load resistor. the second electrode of said sixth active element being 8. A sustain keying circuit as in claim 3 further comprising: grounded, and fourth, fifth and sixth active elements, each having first and 5 the control electrode of said sixth active element being consecond electrodes and a control electrode, nectable to said power source in common with said load said first and second electrodes of said fourth active eler sist rment being connected in series ith th fi t d Second 9. A sustain keying circuit as in claim 1 wherein said active electrodes of said third active element with the control elements comprise field effect transistors with Said first, electrode d h fi t electrode f id f th active 1 10 second and control electrodes corresponding to drain, source ment being connected together to cause the fourth active and K electrodes respectively element to serve as a variable resistance for correcting A sustain keying circuit as in claim 1 wherein said active nonlinearities in the sustain characteristics of said keying elements comprise three'pole diodesch-cuit, and wherein 11. A sustain keying circuit as in claim 1 wherein said active the control electrode of said fifth active element being conelements compflse dnfi'type translswrsnected to the control electrode of Said third active 12. A sustain keying circuit as in claim 1 wherein said active ment, elements comprise alloy-diffused transistors. the first electrode of said fifth active element being com 13. A sustain lteymg circuit as m claim 1 wherein said active nected to the control electrode of said fourth active eleelements compnse mlcroauoy dfiused trans'stors' ment 1F i 

1. In an electronic musical instrument, a sustain keying circuit comprising: an input terminal for receiving an input tone signal from a tone generator, an output terminal for providing a keyed output tone signal having desirable sustain characteristics, first and second active elements, each having first and second electrodes and a control electrode for controlling current flow between said first and second electrodes, said first electrode of said first active element being connected to said second electrode of said second active element, of said first and second active elements being electrically connected togethEr in series and this series arrangement also being connected in series with a load resistor and a power source, said control electrode of said first active element being electrically connected to said input terminal, said load resistor being electrically connected to said output terminal, and keying means including a key-operated switch connected to the control electrode of said second active element, said means producing a controlled tone buildup and a decay sustain characteristic which is produced after key activation and deactivation respectively while yet severely limiting undesirable tone feed through to the output terminal under quiescent circuit conditions.
 2. A sustain keying circuit as in claim 1 wherein said keying means includes a capacitor connected between the control electrode of said second active element and an AC ground.
 3. A sustain keying circuit as in claim 2 wherein said keying means further includes: a third active element having first and second electrodes and a control electrode, said first electrode of said third active element being connected to said control electrode of said second active element, said second electrode of said third active element being electrically connected to one terminal of said power source, and said control electrode of said third active element being connectable to a source of variable voltage whereby the sustain characteristics of said keying circuit may be varied as desired by varying said variable voltage.
 4. A sustain keying circuit as in claim 1 further comprising: a third active element having first and second electrodes and a control electrode, said first and second electrodes of the third active element being electrically connected in series with the first and second electrodes of the first and second active elements, and the control electrode of said third active element being connected in common with the control electrode of the second active element whereby even less undesirable tone feed through is produced while also increasing the reliability of the keying circuit.
 5. A sustain keying circuit as in claim 1 wherein each of said first, second and third active elements is provided with another active element connected in parallel therewith via electrical connections between respectively similar electrodes of each resulting pair of active elements.
 6. A sustain keying circuit as in claim 3 further comprising: fourth and fifth active elements each having first and second electrodes and a control electrode, said first and second electrodes of said fourth active element being connected in series with the first and second electrodes of said third active element, the control electrode and the first electrode of said fourth active element being connected together to cause the fourth active element to serve as a variable resistance for correcting nonlinearities in the sustain characteristics of said keying circuit, and wherein the first and second electrodes of said fifth active element are connected from said control electrode of the fourth active element to groud with the control electrode of the fifth active element connectable to a power source whereby the characteristic decay envelope of the keyed output is exponentially shaped.
 7. A sustain keying circuit as in claim 3 further comprising: fourth and fifth active elements, each having first and second electrodes and a control electrode, said first and second electrodes of said fourth active element being connected in series with the first and second electrodes of said third active element with the control electrode and the first electrode of said fourth active element being connected together to cause the fourth active element to serve as a variable resistance for correcting nonlinearities in the sustain characteristics of said keying circuit, and wherein the first and second electrodes of said fifth active element are connected to the first and second electrodes respectively of the fourth active element with the control electrode of the fifth active element connectable to said power source in common with said load resistor.
 8. A sustain keying circuit as in claim 3 further comprising: fourth, fifth and sixth active elements, each having first and second electrodes and a control electrode, said first and second electrodes of said fourth active element being connected in series with the first and second electrodes of said third active element with the control electrode and the first electrode of said fourth active element being connected together to cause the fourth active element to serve as a variable resistance for correcting nonlinearities in the sustain characteristics of said keying circuit, and wherein the control electrode of said fifth active element being connected to the control electrode of said third active element, the first electrode of said fifth active element being connected to the control electrode of said fourth active element, the second electrode of said fifth active element being connected to the first electrode of said sixth active element, the second electrode of said sixth active element being grounded, and the control electrode of said sixth active element being connectable to said power source in common with said load resistor.
 9. A sustain keying circuit as in claim 1 wherein said active elements comprise field effect transistors with said first, second and control electrodes corresponding to drain, source and gate electrodes respectively.
 10. A sustain keying circuit as in claim 1 wherein said active elements comprise three-pole diodes.
 11. A sustain keying circuit as in claim 1 wherein said active elements comprise drift-type transistors.
 12. A sustain keying circuit as in claim 1 wherein said active elements comprise alloy-diffused transistors.
 13. A sustain keying circuit as in claim 1 wherein said active elements comprise micro alloy diffused transistors. 